In a large saucepan, cook the pancetta over moderately low heat, stirring, until most of the fat has been rendered, about 8 minutes. Add the garlic, carrots, celery, onion, potato, celery root, squash, rutabaga and bay leaf and cook over moderately high heat for 2 minutes, stirring to coat with fat. Season with salt and pepper and cook until the vegetables soften, about 3 minutes longer. Add the chicken stock and bring to a boil. Reduce the heat to low and simmer until the vegetables are tender, about 20 minutes. Discard the bay leaf.